The main aim of the proposed projects is: 1) to investigate whether functional inactivation of the Purkinje (P)-cells of the cerebellar anterior vermis - which project directly to the lateral vestibular nucleus - elicited by intravermal injection of GABA agonists, decreases the response gain of limb extensors to labyrinth stimulation. This finding would indicate that the P-cells of the cerebellar vermis exert a positive influence on the gain of the vestibulospinal (VS) reflex; 2) to verify the hypothesis that the cholinergic (as well as the noradrenergic) systems projecting to the cerebellar cortex regulate information processing by increasing the amplitude of the P-cell responses to locally applied pulses of glutamate, the excitatory neurotransmitter of the mossy fibers - parallel fibers system; 3) to investigate whether sustained rotation about the longitudinal axis of the whole animal leading to stimulation of labyrinth receptors, associated with a sustained outphase or inphase neck rotation, produces plastic events characterized by a long-term adaptive increase or decrease in gain of the VS reflex. Finally, 4) to investigate the consequences of unilateral labyrinthectomy at the molecular level, by exploring the effects of this lesion on the induction of immediate early genes, such as c-fos, which can function as "third messengers" and of some of their protein products. The identification of specific changes of the third messengers expression in specific regions of the brain would open the way to the investigation of subsequent molecular steps involved in the regulation of vestibular functions.